3. Notes of the Above Methods 184-196 Sampling 183 Moisture and Volatile Matter 184-187 Insoluble Impurities 187 Soluble Mineral Matter 187-188 Free Fatty Acid 188-189 Titer 189 Unsaponified Matter 190-193 Melting Point 193-196 Plant and Machinery 198-219 Illustrations of Machinery and Layouts of the Plant of a Modern Soap Making Establishment 198-219 Appendix 219-237 Useful Tables Index 239 CHAPTER I Raw Materials Used in Soap Making. Soap is ordinarily thought of as the common cleansing agent well known to everyone. In a general and strictly chemical sense this term is applied to the salts of the non-volatile fatty acids. These salts are not only those formed by the alkali metals, sodium and potassium, but also those formed by the heavy metals and alkaline earths. Thus we have the insoluble soaps of lime and magnesia formed when we attempt to wash in "hard water"; again aluminum soaps are used extensively in polishing materials and to thicken lubricating oils; ammonia or "benzine" soaps are employed among the dry cleaners. Commonly, however, when we speak of soap we limit it to the sodium or potassium salt of a higher fatty acid. It is very generally known that soap is made by combining a fat or oil with a water solution of sodium hydroxide (caustic soda lye), or potassium hydroxide (caustic potash). Sodium soaps are always harder than potassium soaps, provided the same fat or oil is used in both cases. The detergent properties of soap are due to the fact that it acts as an alkali regulator, that is, when water comes into contact with soap, it undergoes what is called hydrolytic dissociation. This means that it is broken down by water into other substances. Just what these substances are is subject to controversy, though it is presumed caustic alkali and the acid alkali salt of the fatty acids are formed. OILS AND FATS. There is no sharp distinction between fat and oil. By "oil" the layman has the impression of a liquid which at warm temperature will flow as a slippery, lubricating, viscous fluid; by "fat" he understands a greasy, solid substance unctuous to the touch. It thus becomes necessary to differentiate the oils and fats used in the manufacture of soap.